1. Field of the Invention
This invention relates to catheter tipping, and more particularly relates to facilitating release of a tipping die from a tipped catheter.
2. Background of the Invention
Intravenous (I.V.) catheters are extensively used in medical applications for directing blood, plasma, or other fluids into the circulatory system of a patient. While I.V. catheters are available in several different types, one common type of catheter is constructed so as to be mounted upon a relatively long, hollow cannula with a slight friction fit. A hub is attached at one end of the catheter and is designed so as to be connectable with and detachable from an I.V. fluid supply line. To insert the catheter into the patient, the cannula and catheter together are inserted through the patient's skin, whereupon the cannula may be withdrawn, leaving the catheter in place.
Untipped catheter tubing as extruded (hereinafter referred to as blank) is unsuitable for insertion through the skin of the patient because it has blunt ends which cause pain, trauma and irritation to the surrounding tissue. Accordingly, it is conventional to provide a tapered tip for insertion. Further, if the catheter is to remain in position for a long period of time, it is more comfortable for the patient if it is made of a relatively soft pliable material. Because it is soft and pliable, the catheter is generally used with a removable introducer needle fitted coaxially within the catheter in order to puncture the skin and penetrate the vessel. The introducer needle needs to project slightly beyond the end of the catheter so that, shortly after the introducer needle has pierced the skin of the patient, the catheter may then pass through the same perforation. Once the catheter has been slid along the needle into position, the introducer needle can then be removed by coaxially withdrawing the needle from within the inserted catheter.
It has been a problem with devices of this type to produce a catheter having a tapered tip which permits insertion over the introducer needle. More specifically, the catheter body has to be of high strength and thin wall in order to permit maximum fluid flow yet the tip requires a specific design to permit ease of introduction along with the needle.
Daugherty et al. discloses in U.S. Pat. No. 4,588,398 a catheter tip configuration for over-the-needle polyurethane catheters having a steep bevel at the distal end of the tip and a shallow bevel immediately above the steep bevel. The patented catheter tip and whole catheter are lubricated with a mixture of DC 360.RTM. polydimethylsiloxane (Dow Chemical) and Dow 4-4159MDX (a moisture curable amine terminated polysiloxane disclosed in U.S. Pat. No. 3,574,673, hereinafter referred to as MDX) to ease catheter insertion through a venipuncture created by the needle. In U.S. Pat. No. 4,661,300, hereby incorporated by reference, Daugherty discloses an apparatus for catheter tipping which includes a mandrel and a heated die. A silicone prelubricated catheter blank on the mandrel is shaped by the die and cut externally of the die to provide the tip.
Williamitis et al., in U.S. Pat. No. 4,664,657, lubricates a catheter assembly at the cannula (needle) tip with a polydimethylsiloxane having a viscosity in the range of 60,000 to 2,500,000 centistokes (ctsk). On mating of the cannula by interference fit with a catheter, reduction in the development of time-temperature adhesion between the catheter and cannula tip is achieved.
For catheter tipping, the purpose of the lubricant is to prevent catheter adhesion to the forming die and mandrel at the near melt temperature of tipping. While it is known in the art to lubricate cannulas, catheters and dies, the lubricants which have been disclosed for this purpose have various deficiencies.
Polydimethylsiloxane silicone oils have been used as lubricants in catheter tipping. These products, however, have the disadvantage of being easily wiped away. Formulas based on the organopolysiloxanes described in U.S. Pat. No. 3,574,673 and disclosed for catheter tipping in U.S. Pat. No. 4,588,398, have hitherto been the best die release agent. These products, such as MDX, are copolymers of alkylamine modified methoxysiloxanes and undergo room temperature vulcanization (RTV) to a gelatinous film. These organosiloxanes are referred to as gelling siloxanes and, depending on ambient humidity, require at least a four-hour precure of the coating applied to a catheter blank prior to tipping, and further require from two to ten days for full cure. In addition, solvent solutions of MDX, used for application of the MDX to catheter blanks by dipping, quickly turn cloudy due to precipitated polymer from reaction of the MDX with humidity in the air. During a tipping operation, these solutions must be replaced frequently to prevent buildup of cured MDX on the tipping die, which is time consuming, wasteful and costly. These constraints are a severe limitation to use of the formulations of U.S. Pat. No. 3,574,673 for catheter tipping.
Thus, there is a need in the art for a method for tipping polyurethane catheters which avoids the limitations imposed on prior art tipping methods by the hitherto disclosed die releasing lubricants.